Is it possible to mount the NTFS and registry hives from a 64-bit Windows on a 32-bit Windows Preinstallation Environment (32-bit). Does 64-bit change the file format?
Also can x86_64 machines boot unmodified 32-bit OSes?
There's no overall data/schema differences between the registries of 32-bit and 64-bit Windows - obviously the actual content will be different but there's no structural differences no.
And yes an x86 64-bit machine can 100% boot a 32-bit OS straight out of the box.
NTFS is the same for 32- and 64-bit, so you will be able to read any files.
As for the structure -
so, your offline editor shall be capable of viewing/changing both parts.